The Geologic History of Fossil Butte National Monument and Fossil Basin
NPS Occasional Paper No. 3
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ANAEROBIC. Usually in reference to organisms that can live without oxygen.

ANGULAR UNCONFORMITY. Two rock layers which are not parallel; the underlying older layer dips at a different angle (usually steeper) than the younger top strata.

ANNULI. Marks on fish scales produced by periods (usually winter) of nongrowth.

ANTICLINE. A fold in stratified rock with the strata sloping downward in opposite directions from the fold crest.

AUTHIGENIC. A mineral (such as quartz or feldspar) which is formed after the deposition of a sedimentary layer in which it occurs.

ARAGONITE. A carbonate mineral with specific characteristics.

BENTONITE. A light-colored, soft, porous rock formed from the minute clay crystals of eroded volcanic ash. It has the characteristic of swelling when wet (water absorption) and contracting when dry.

BRACKISH. A condition in a body of water in which the salinity (salt level) is below that of sea water, but higher than that of fresh water.

CARBONACEOUS. Rock or sediment which contains carbon or altered organic material such as coal.

CHERTY. Containing chert; a dull-colored, flint-like quartz often found in limestone.

CIRCULI. Ridges on fish scales produced during growth of the scales.

CLAST. Rock fragments which are the result of weathering of a larger rock mass.

CLASTIC. Rocks that consist of particles derived from pre-existing rocks or minerals.

CLAYSTONE. An indurated clay without the lamination or fissility of shale.

CONGLOMERATE. A coarse-grained sedimentary rock composed of fragments larger than 2 mm in diameter in a fine-grained matrix.

CROSS-BEDDING. An internal structure in sedimentary rock in which the upper sedimentary layer runs across the grain of the main bed; it is caused by changing currents depositing sediment across the grain of the original deposits.

DIAMICTITE. A sedimentary rock containing a wide range of particle sizes.

DIP. The downward inclination of a rock layer; the vertical angle is determined by its relationship to a horizontal plane.

DOLOMITIC. Containing a measurable amount of the mineral dolomite; a mineral consisting mainly of magnesium carbonate and calcium carbonate.

FACIES. Lateral variations in the appearance or composition of a rock layer. The variations can be lithologic or paleontologic.

FAULT. A fracture in the earth's crust along which displacement (movement) has occurred.

FLUVIAL. Pertaining to a river or rivers. Fluvial sediments are those transported and deposited by stream action.

FORMATION. A rock layer that is mappable; has a distinctive lithology or series of lithologies. A mappable sequence of uniform or uniformly varying rocks.

GASTROPODAL. A rock containing an abundance of gastropods.

HOGBACK. A long, narrow, sharp-crested ridge formed by the outcropping edges of steeply inclined resistant rocks.

IGNEOUS ROCKS. A rock or mineral that has solidified from molten or partly molten material.

INTRUSIVE. Igneous rock formed by the forcing of molten material into a pre-existing rock.

IRONSTONE. A rock composed of various iron minerals that accumulated during or shortly after deposition of the enclosing sediments.

LACUSTRINE. Pertaining to, produced by, or formed in a lake or lakes.

LATERITIC. Containing laterite: a red, porous material usually developed in a tropical to temperate climate. It is a residual or end-product of weathering.

LIGNITE. A brownish-black coal that is intermediate in coalification between peat and subbituminous coal.

LITHOLOGY. The scientific study of rocks: composition, texture, color, origin, etc.

MAGNETITE. A black, opaque mineral that is strongly magnetic.

MARLSTONE. An impure limestone.

METAMORPHIC. Rocks whose structure has been changed by pressure, heat, chemical reaction, etc., such as limestone into marble.

MUDSTONE. An indurated mud without the lamination or fissility of shale.

OPERCULAR OPENING. The gill opening of fish.

OSTRACODAL. A rock, usually a limestone, that contains an abundance of the small crustacean, ostracods.

OVERTHRUST. A low-angle thrust fault of large scale, usually measured in miles.

PALEOLIMNOLOGY. The study of ancient lakes.

PAPER SHALE. A form of finely laminated shale that weathers into extremely thin, curled flakes.

PHOSPHATIC. Containing phosphates.

PHYTOPLANKTON. Floating microscopic plant life that occurs abundantly in lakes and oceans.

PLATY. Rocks (sandstone or limestone) which separate into small slabs.

PORCELLANITE. A dense cherty rock resembling porcelain.

PUDDINGSTONE. A conglomerate consisting of well-rounded pebbles and cobbles sparsely packed in a fine-grained matrix.

SILTSTONE. An indurated silt without the lamination or fissility of shale.

STRATA. Rock layers of distinct composition and origin.

SYNCLINE. A fold in stratified rock in which the strata slope up from the axis of the fold forming a V opposed to anticline.

TAPHONOMY. The branch of paleoecology which deals with the change from living animals to fossils.

TECTONIC. The forces which result in structural changes in the earth's crust.

THRUST FAULT. A fault in which an upper segment of rock (hanging wall) moves upward at a low angle (less than 45°) relative to a lower segment (footwall).

TONGUE. A rock unit that wedges into, but disappears within, another rock unit.

TUFFACEOUS. Sediment that contains up to 50% volcanic ash or dust.

UNCONFORMITY. A substantial break or gap in the geologic or stratigraphic record.

UNGULATES. Hooved mammals.

VARVE. A set of rock laminae in which different types of sediment were deposited in the winter and in the summer. Thus a couplet of each sediment type would represent the deposition of one year.

WELL SORTED. A rock in which nearly all of the sediment particles are of one grain size.

ZOOPLANKTON. Floating microscopic animal life that occurs abundantly in lakes and oceans.

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Last Updated: 01-Mar-2005